Image processing apparatus, image display apparatus and image display system

ABSTRACT

Disclosed herein is a video-image processing apparatus including: a video-image processing section configured to execute output control on video-image streams each including unitary video images appearing along the time axis so as to output every unitary video image pertaining to each of the video-image streams repeatedly a plurality of times by sequentially switching the video-image streams to be output on a time-division basis; a frame memory for temporarily storing an immediately preceding unitary video image as it is or after replacing the luminance gradation of the immediately preceding unitary video image with a post-replacement luminance gradation where the immediately preceding unitary video image is defined as a unitary video image which immediately leads ahead of a current unitary video image being output by the video-image processing section and is selected; and an overdrive processing section configured to carry out overdrive processing on the current unitary video image.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation, of U.S. patent applicationSer. No. 12/800,338, filed May 13, 2010, which claims priority fromJapanese Patent Application No. P2009-136354 filed in the JapanesePatent Office on Jun. 5, 2009, the disclosures of which are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a video-image processing apparatus forcarrying out overdrive processing on an input video-image signal, avideo-image display apparatus employing the video-image processingapparatus and a video-image display system including the video-imagedisplay apparatus.

2. Description of the Related Art

In recent years, an LCD (Liquid Crystal Display) apparatus of theactive-matrix type is used widely as the image display section of a thinTV or the image display section of a portable terminal. The LCDapparatus employs a TFT (Thin Film Transistor) for each pixel of the LCDapparatus. Pixels employed in such an LCD apparatus are arranged to forma matrix including rows on the display screen of the LCD apparatus. Ingeneral, every pixel is driven by writing a video-image signalsequentially on a row-after-row basis into an auxiliary capacitor and aliquid-crystal device which are employed in the pixel in a directionfrom the top of the display screen to the bottom thereof.

By the way, depending on the application of the LCD apparatus, one frameperiod is divided into a number of sub-periods and the LCD apparatus isdriven in a driving operation referred to hereafter as a time-divisiondriving operation in order to display a video image which varies fromsub-period to sub-period. A method adopted to carry out a time-divisiondriving operation is referred to as a time-division driving method.Typical examples of an LCD apparatus adopting the time-division drivingmethod are an LCD apparatus disclosed in documents such as JapanesePatent Laid-Open No. 2001-318363 in which a field sequential method isadopted and a 3D (3 Dimensional) image display system disclosed indocuments such as Japanese Patent Laid-Open Nos. Hei 9-138384,2000-36969 and 2003-45343 in which the so-called shutter glasses areused.

The field sequential method is a driving method, in accordance withwhich one frame period is divided into three frame sub-periods allocatedto operations to sequentially write R (red), G (green) and B (blue)video-image signals respectively into pixels. In addition, in accordancewith the field sequential method, the R, G and B light rays are emittedfrom a backlight synchronously with the R, G and B video-image signalsrespectively. In an ordinary LCD apparatus, a pixel is generally dividedinto R, G and B sub-pixels which are laid out spatially. Thus, theefficiency of the utilization of light is poor. By adopting the fieldsequential driving method, however, the efficiency of the utilization oflight can be improved.

In the 3D image display system making use of shutter glasses, on theother hand, one frame period is divided into two frame sub-periodsallocated to operations to alternately display two video images providedfor the left and right eyes respectively as images having a disparityrecognized by the left and right eyes. The 3D image display system makesuse of shutter glasses which are switched to close the left eye and openthe right eye and vice versa synchronously with the operations toalternately display the two video images provided for the left and righteyes. The viewer views a displayed image by wearing the switched shutterglasses which allow the image to be seen by the viewer as a 3D image.

SUMMARY OF THE INVENTION

In some cases, however, in an LCD apparatus adopting any of thetime-division driving methods described above, consecutive video imagesare inadvertently mixed with each other in a phenomenon referred to asan interference or crosstalk. If crosstalk occurs, the color of an imagedisplayed on a screen in accordance with the field sequential methodappears differently from the true one. If crosstalk occurs in the 3Dimage display system making use of shutter glasses, on the other hand,at the top of the display screen and/or the bottom thereof, theright-hand side portion of an image displayed on the screen is seen bythe left eye whereas the left-hand side portion of the displayed imageis seen by the right eye or vice versa so that the correct 3D videoimage can hardly be recognized. In general, in the time-division drivingmethod, every pixel is driven by writing a video-image signalsequentially on a row-after-row basis into the pixel in a direction fromthe top of the display screen to the bottom thereof. As a result, muchcrosstalk occurs at the top and bottom of the display screen.

Such crosstalk is generated because of poor characteristics of the LCDapparatus and/or poor characteristics of shutter glasses which are eachprovided with a light shielding shutter. Poor characteristics of the LCDapparatus include an inadequate response speed of the apparatus whereaspoor characteristics of shutter glasses include insufficient shuttercontrasts.

In order to solve the problems described above, a continuous writingmethod has been conceived. In accordance with this continuous writingmethod, first of all, a video-image signal is written into pixelscontinuously within one frame period in units each including a pluralityof unitary video images in an operation to continuously write thevideo-image signal into the pixels. Then, during a period in which adesired luminance level is sustained by virtue of sufficient responsesprovided by liquid-crystal devices included in the pixels to theoperation to continuously write the video-image signal into the pixels,the backlight is turned on and a light shielding shutter employed in theshutter glasses is put in an open state to be described more later.Thus, the backlight can be turned on or the light shielding shutter canbe put in an open state only during a period in which the same videoimage is being displayed on the entire screen. As a result, crosstalkcan be conceivably suppressed.

In addition, in order to compensate the LCD apparatus for the inadequateresponse speed of liquid-crystal devices employed in the apparatus,overdrive processing has been proposed in the past. For more informationon the overdrive processing, the reader is suggested to refer todocuments such as Japanese Patent Laid-Open No. 2005-107531. During anoperation to display a video image in accordance with the time-divisiondriving method such any of the ones described above, a plurality ofvideo images are always displayed repeatedly so that the liquid-crystaldevices never get settled in a steady state in many cases. Thus, if theexisting overdrive processing premising a transition from the steadystate is applied as it is to a video-image display operation carried outby adoption of the time-division driving method, the optimum level of anapplied voltage cannot be obtained so that a shift from target luminanceis inevitably resulted in. As a result, crosstalk is undesirablygenerated.

In addition, if the existing overdrive processing is applied as it is toa video-image display operation carried out by adoption of thecontinuous writing method, for every continuous writing operation,overdrive processing is carried out always in accordance with theluminance gradation of the current unitary video image and the luminancegradation of a unitary video image immediately leading ahead of thecurrent unitary video image regardless of whether or not the currentunitary video image and the unitary video image immediately leadingahead of the current unitary video image are the same video image orpertain to the same video-image stream. Thus, since the function of theoverdrive processing cannot be executed fully, a shift from targetluminance is resulted in similarly. As a result, crosstalk isundesirably generated.

As described above, in accordance with the existing techniques, in anoperation to display a video image by adoption of the time-divisiondriving method, it is not possible to avoid generation of crosstalkamong a plurality of successive video images. Thus, implementation of animproved technique is desirable. It is to be noted that the problemseach described so far as a problem of crosstalk are raised not only byan LCD apparatus. That is to say, the crosstalk problems can also beraised by a video-image display apparatus of another kind.

Addressing the problems described above, inventors of the presentinvention have innovated a video-image processing apparatus capable ofeliminating crosstalk which appears as interferences among a pluralityof successive video images. The inventors have also innovated avideo-image display apparatus employing the video-image processingapparatus and a video-image display system including the video-imagedisplay apparatus.

A video-image processing apparatus according to an embodiment of thepresent invention includes:

a video-image processing section configured to execute output control ona plurality of video-image streams each including a plurality of unitaryvideo images appearing along the time axis so as to output every unitaryvideo image pertaining to each of the video-image streams repeatedly aplurality of times in a row by sequentially switching the video-imagestreams to be output from one stream to another on a time-divisionbasis;

a frame memory for temporarily storing an immediately preceding unitaryvideo image as it is or after replacing the luminance gradation of theimmediately preceding unitary video image with a post-replacementluminance gradation where the immediately preceding unitary video imageis defined as a unitary video image which immediately leads ahead of acurrent unitary video image being output by the video-image processingsection and is selected among unitary video images pertaining to avideo-image stream other than and different from a video-image streamincluding the current unitary video image; and

an overdrive processing section configured to carry out overdriveprocessing on the current unitary video image in accordance with theluminance gradation of the immediately preceding unitary video imagealready stored in the frame memory and the luminance gradation of thecurrent unitary video image.

The technical term “video-image stream” used in the above descriptionmeans a sequence of unitary video images consecutively appearing on thetime axis. Typical examples of the video-image stream are a left-eyevideo-image stream and a right-eye video-image stream which are outputin an operation to display 3D video images. In the case of a video-imagestream having a frequency of 60 Hz, for example, static video images aredisplayed continuously one image after another at a frequency of 60 Hzor a rate of 60 images per second. Each of the static images is referredto as the unitary video image mentioned above.

A video-image display apparatus according to an embodiment of thepresent invention employs the video-image processing apparatus providedby the embodiment of the present invention as described above and avideo-image display section for displaying a video image on the basis ofunitary video images completing the overdrive processing carried out bythe video-image processing apparatus.

A video-image display system includes:

the video-image display apparatus provided by the embodiment of thepresent invention, for displaying a video image by sequentiallyswitching a plurality of video-image streams each including a pluralityof unitary video images appearing along the time axis from one stream toanother on a time-division basis; and

shutter glasses carrying out opening and closing operationssynchronously with operations performed by the video-image displayapparatus to sequentially switch the video-image streams in order todisplay the video image.

In the video-image processing apparatus, the video-image displayapparatus and the video-image display system which are provided byembodiments of the present invention, the video-image processing sectionexecutes output control on a plurality of video-image streams eachincluding a plurality of unitary video images appearing along the timeaxis so as to output every unitary video image pertaining to each of thevideo-image streams repeatedly a plurality of times in a row within apredetermined period of time by sequentially switching the video-imagestreams to be output from one stream to another on a time-division basiswithin the predetermined period of time.

In addition, the frame memory is used for temporarily storing animmediately preceding unitary video image as it is or after replacingthe luminance gradation of the immediately preceding unitary video imagewith a post-replacement luminance gradation before the immediatelypreceding unitary video image is stored in the frame memory. In thiscase, the immediately preceding unitary video image is defined as aunitary video image which immediately leads ahead of a current unitaryvideo image being output by the video-image processing section and isselected among unitary video images pertaining to a video-image streamother than and different from a video-image stream including the currentunitary video image.

Then, the overdrive processing section carries out overdrive processingon the current unitary video image in accordance with the luminancegradation of the immediately preceding unitary video image alreadystored in the frame memory and the luminance gradation of the currentunitary video image itself.

In the existing video-image display system, the overdrive processing iscarried out to output unitary video images pertaining to each of thevideo-image streams consecutively in a predetermined period of timealways in accordance with the luminance gradation of the current unitaryvideo image and the luminance gradation of a unitary video imageimmediately leading ahead of the current unitary video image regardlessof whether or not the current unitary video image and the unitary videoimage immediately leading ahead of the current unitary video image isthe same unitary video image or pertain to the same video-image stream.Thus, in comparison with the existing video-image display system,according to the present invention, it is possible to reduce themagnitude of a shift of a display luminance based on unitary videoimages completing the overdrive processing from a target luminance.

In accordance with the video-image processing apparatus, the video-imagedisplay apparatus and the video-image display system which are providedby the present invention, the frame memory is used for temporarilystoring an immediately preceding unitary video image as it is or afterreplacing the luminance gradation of the immediately preceding unitaryvideo image with another gradation before the immediately precedingunitary video image is stored in the frame memory. In this case, theimmediately preceding unitary video image is defined as a unitary videoimage which immediately leads ahead of a current unitary video imagebeing output by the video-image processing section and is selected amongunitary video images pertaining to a video-image stream other than anddifferent from a video-image stream including the current unitary videoimage. Then, the overdrive processing section carries out overdriveprocessing on the current unitary video image in accordance with theluminance gradation of the immediately preceding unitary video imagealready stored in the frame memory and the luminance gradation of thecurrent unitary video image itself. Thus, in comparison with theexisting video-image display system, according to an embodiment of thepresent invention, it is possible to reduce the magnitude of a shift ofa display luminance based on unitary video images completing theoverdrive processing from a target luminance. As a result, it ispossible to reduce crosstalk which appears as interferences among aplurality of consecutive unitary video images. It is to be noted that,as described above, in the existing video-image display system, theoverdrive processing is carried out in order to output unitary videoimages pertaining to each of the video-image streams consecutively oneimage after another in a predetermined period of time always inaccordance with the luminance gradation of the current unitary videoimage and the luminance gradation of a unitary video image immediatelyleading ahead of the current unitary video image regardless of whetheror not the current unitary video image and the unitary video imageimmediately leading ahead of the current unitary video image pertain tothe same video-image stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the entire configuration of avideo-image display system employing a video-image display apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a circuit diagram showing details of a typical configurationof every pixel employed in the video-image display apparatus shown inFIG. 1;

FIGS. 3A and 3B are model diagrams each showing a typical LUT (Look-UpTable) used in overdrive processing;

FIGS. 4A and 4B are model diagrams each to be referred to in explanationof a 3D video-image displaying operation carried out by the video-imagedisplay system shown in FIG. 1;

FIGS. 5A and 5B are timing diagrams to be referred to in explanation ofcrosstalk that can be generated in an operation carried out by theexisting video-image display apparatus to display a 3D video image;

FIGS. 6A and 6B are timing diagrams to be referred to in explanation ofan outline of an operation carried out by the video-image display systemshown in FIG. 1 to display a 3D video image;

FIGS. 7A to 7C are timing diagrams to be referred to in explanation oftypical overdrive processing provided for a comparison purpose;

FIG. 8 is a diagram showing typical response characteristics of thedisplay luminance in the course of execution of the overdrive processingshown in FIGS. 7A to 7C;

FIGS. 9A to 9C are timing diagrams to be referred to in explanation ofoverdrive processing carried out by the first embodiment;

FIG. 10 is a timing diagram showing typical response characteristics ofthe display luminance in the course of execution of the overdriveprocessing shown in FIGS. 9A to 9C;

FIGS. 11A to 11C are timing diagrams to be referred to in explanation ofoverdrive processing carried out by a second embodiment of the presentinvention;

FIG. 12 is a diagram showing a typical replacement-value lookup tableused in the second embodiment;

FIG. 13 is a timing diagram showing a typical response characteristic ofthe display luminance in the course of execution of the overdriveprocessing shown in FIGS. 11A to 11C;

FIGS. 14A to 14C are timing diagrams to be referred to in explanation ofoverdrive processing carried out by a first modified version of thepresent invention;

FIGS. 15A to 15C are timing diagrams to be referred to in explanation ofoverdrive processing carried out by a second modified version of thepresent invention; and

FIGS. 16A and 16B are model diagrams each to be referred to inexplanation of an outline of an operation carried out by a video-imagedisplay system according to a third modified version of the presentinvention to display a 3D video image.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

Preferred embodiments of the present invention are described below indetail by referring to the diagrams. It is to be noted that theembodiments are explained in chapters which are arranged in thefollowing order.

1: First Embodiment

(for displaying a 3D video image by using two overdrive-processing LUTs)

2: Second Embodiment

(for displaying a 3D video image by further using a replacement-valueLUT)

3: Modified Versions

3-1: First Modified Version (for displaying a 3D video image by usingthree overdrive-processing LUTs) and Second Modified Version (fordisplaying a 3D video image by further using a replacement-value LUT)

3-2: Third Modified Version (application to a multi-video-image displaysystem)

3-3: Other Modified Versions

1: First Embodiment 1-1: Entire Configuration of a Video-Image DisplaySystem

FIG. 1 is a block diagram showing the entire configuration of avideo-image display system employing a video-image display apparatusaccording to a first embodiment of the present invention. Thevideo-image display system is a video-image display system which adoptsthe time-division driving method. As shown in FIG. 1, the video-imagedisplay system employs a liquid-crystal display apparatus 1, whichserves as the video-image display apparatus according to the firstembodiment of the present invention and shutter glasses 6.

1-1-1: Liquid-Crystal Display Apparatus 1

The liquid-crystal display apparatus 1 is an apparatus for displaying avideo image on the basis of an input video-image signal Din whichincludes a right-eye video-image signal DR serving as a video-imagesignal for the right eye and a left-eye video-image signal DL serving asa video-image signal for the left eye. The right-eye video-image signalDR represents video-image signals included in a video-image stream forthe right eye whereas the left-eye video-image signal DL representsvideo-image signals included in a video-image stream for the left eye.The right-eye video-image signal DR and the left-eye video-image signalDL have a disparity.

As shown in FIG. 1, the liquid-crystal display apparatus 1 employs aliquid-crystal display panel 2, a backlight 3, a video-image signalprocessing section 41, a frame memory 42, a shutter control section 43,an overdrive processing section 44, a timing control section 45, abacklight driving section 50, a data driver 51 and a gate driver 52. Thevideo-image signal processing section 41, the frame memory 42 and theoverdrive processing section 44 together form a typical implementationof a video-image processing apparatus provided by the present invention.

The backlight 3 is a light source for radiating light to theliquid-crystal display panel 2. Typically, the backlight 3 is configuredto include LEDs (Light Emitting Diodes) or CCFL (Cold CathodeFluorescent Lamps).

In accordance with driving signals received from the gate driver 52 andon the basis of video-image voltages received from the data driver 51,the liquid-crystal display panel 2 modulates the light, which isradiated by the backlight 3 to the liquid-crystal display panel 2, inorder to display a video image based on the input video-image signalDin. To put it more concretely, the liquid-crystal display panel 2displays a right-eye video image based on the right-eye video-imagesignal DR and a left-eye video image based on the left-eye video-imagesignal DL alternately on a time-division basis as will be describedlater in detail. The right-eye video images based on the right-eyevideo-image signal DR are right-eye unitary video images pertaining tothe video-image stream for the right eye whereas the left-eye videoimages based on the left-eye video-image signal DL are left-eye unitaryvideo images pertaining to the video-image stream for the left eye. Thatis to say, a time-division driving operation to display a 3D video imageis an operation carried out to display the 3D video image on theliquid-crystal display panel 2 in an output order controlled by thevideo-image signal processing section 41 to be explained later. Theliquid-crystal display panel 2 is configured to include a plurality ofpixels 20 which are all laid out to form a matrix. It is to be notedthat a detailed configuration of the pixel 20 will be described byreferring to a circuit diagram of FIG. 2.

The video-image signal processing section 41 controls the aforementionedoutput order (also referred to as a write order) of the right-eyevideo-image signal DR and the left-eye video-image signal DL in order togenerate a video-image signal D1. To put it more concretely, thevideo-image signal processing section 41 controls the output order sothat, while the video-image streams are being output by beingsequentially switched from one stream to another on a time-divisionbasis in one frame period, the right-eye video-image signal DR and theleft-eye video-image signal DL each are output a plurality of times in arow during the frame period. In the case of the first embodiment, theright-eye video-image signal DR and the left-eye video-image signal DLare each output two times in a row during one frame period. To put itmore concretely, in one frame period, the video-image signal processingsection 41 produces the video-image signal D1 in accordance with thefollowing order: a left-eye video-image signal DL→a left-eye video-imagesignal DL→a right-eye video-image signal DR→a right-eye video-imagesignal DR. In particular, a sub-period included in one frame period toserve as a sub-period allocated to an operation to output a left-eyevideo-image signal DL two times in a row is referred to as an L framesub-period whereas a sub-period included in one frame period to serve asa sub-period allocated to an operation to output a right-eye video-imagesignal DR two times in a row is referred to as an R frame sub-period.

The frame memory 42 is a memory used for temporarily storing avideo-image signal based on the input video-image signal Din. To put itmore concretely, the frame memory 42 receives the signal of animmediately preceding unitary video image from the video-image signalprocessing section 41 and is used for storing the signal. Theimmediately preceding unitary video image is a unitary video imageappearing in a frame sub-period which immediately leads ahead of thecurrent frame sub-period. The frame memory 42 is used for storing thesignal of the immediately preceding unitary video image as it is withoutprocessing the signal in the video-image signal processing section 41during the frame sub-period which immediately leads ahead of the currentframe sub-period.

To put it more concretely, for example, let the current frame sub-periodbe an L frame sub-period. In this case, a frame sub-period leading aheadof the current L frame sub-period is an R frame sub-period in. Thus, inthe L frame sub-period serving as the current frame sub-period, theright-eye video-image signal DR appearing in the R frame sub-period isalways selected and stored in the frame memory 42.

If the current frame sub-period is an R frame sub-period, on the otherhand, a frame sub-period leading ahead of the current R frame sub-periodis an L frame sub-period. Thus, in the R frame sub-period serving as thecurrent frame sub-period, the left-eye video-image signal DL appearingin the L frame sub-period is always selected and stored in the framememory 42.

It is to be noted that a variety of memories, for example, an SRAM(Static Random Access Memory) can be used as the frame memory 42.

The shutter control section 43 is a section for supplying a timingcontrol signal CTL to the shutter glasses 6 to be described later inaccordance with timing control executed by the video-image signalprocessing section 41. The control signal CTL is a signal forcontrolling operations of light shielding shutters employed in theshutter glasses 6 synchronously with timings to display video images forthe left and right eyes. It is to be noted that, in the case of thefirst embodiment, the control signal CTL is typically a radio signalsuch as an infrared ray signal. However, the control signal CTL is by nomeans limited to a radio signal. For example, the control signal CTL canalso be a wire signal.

The overdrive processing section 44 is a section for carrying outoverdrive processing on a current unitary video-image signal D1 (aunitary video-image signal) in accordance with the luminance gradationof the immediately preceding unitary video-image signal D2 (alsoreferred to as a stored unitary video-image signal) already stored inthe frame memory 42 and the luminance gradation of the current unitaryvideo-image signal D1 itself.

Each of the left-eye video-image signal DL and the right-eye video-imagesignal DR is output two times in a row in two consecutive writeoperations respectively. Every time a left-eye video-image signal DL ora right-eye video-image signal DR is output, the overdrive processingsection 44 carries out overdrive processing on the left-eye video-imagesignal DL or the right-eye video-image signal DR by making use of theluminance gradation of the left-eye video-image signal DL or theright-eye video-image signal DR itself and making use of the luminancegradation of an immediately preceding video-image signal immediatelyleading ahead of the left-eye video-image signal DL or the right-eyevideo-image signal DR as a luminance gradation common to the left-eyevideo-image signal DL and the right-eye video-image signal DR or commonto the two consecutive write operations. The immediately precedingvideo-image signal immediately leading ahead of the left-eye video-imagesignal DL or the right-eye video-image signal DR is a video-image signalpertaining to an immediately preceding video-signal stream other thanand different from the current video-signal stream. The overdriveprocessing can be carried out in the current frame sub-period by makinguse of the luminance gradation of the immediately preceding video-imagesignal output during a video-image stream leading ahead of the currentvideo-signal stream because the immediately preceding video-image signalhas been stored in the frame memory 42 as explained before.

For example, let the current frame sub-period be an L frame sub-periodwhich is further divided into first and second L frame sub-sub-periods.In this case, for the left-eye video-image signal DL output two times ina row during the first and second L frame sub-sub-periods of the currentL frame sub-period, the overdrive processing section 44 carries outoverdrive processing on the left-eye video-image signal DL output twotimes in a row during the first and second L frame sub-sub-periods bymaking use of the luminance gradation of an immediately precedingright-eye video-image signal DR output in the immediately preceding Rframe sub-period immediately leading ahead of the current L framesub-period as a luminance gradation common to the first and second Lframe sub-sub-periods.

If the current frame sub-period is an R frame sub-period which isfurther divided into first and second R frame sub-sub-periods, on theother hand, for the right-eye video-image signal DR output two times ina row during the first and second R frame sub-sub-periods of the currentR frame sub-period, the overdrive processing section 44 carries outoverdrive processing on the right-eye video-image signal DR output twotimes in a row during the first and second R frame sub-sub-periods bymaking use of the luminance gradation of an immediately precedingleft-eye video-image signal DL output in the immediately preceding Lframe sub-period immediately leading ahead of the current R framesub-period as a luminance gradation common to the first and second Rframe sub-sub-periods.

Every time a video-image signal included in the video-image signal D1 isoutput two times in a row during first and second frame sub-sub-periodsas described above, in the overdrive processing, the overdriveprocessing section 44 makes use of two different LUTs (Look-Up Tables)each prescribing overdrive quantities for the first and second framesub-sub-periods respectively. That is to say, when the video-imagesignal included in the video-image signal D1 is output to (written into)pixels during the first frame sub-sub-period, the overdrive processingsection 44 refers to the first LUT in order to find a first overdrivequantity by making use of the luminance gradation common to the firstand second frame sub-sub-periods. When the video-image signal includedin the video-image signal D1 is output to (written into) pixels duringthe second frame sub-sub-period, on the other hand, the overdriveprocessing section 44 refers to the second LUT different from the firstLUT in order to find a second overdrive quantity, which is differentfrom the first overdrive quantity, also by making use of the luminancegradation common to the first and second frame sub-sub-periods. The twoLUTs are each used for prescribing overdrive quantities set inaccordance with the luminance gradations of the video-image signal D1and the immediately preceding video-image signal D2 which have beendescribed before. An overdrive quantity prescribed in such an LUT isused as the luminance gradation of a video-image signal D3 which is avideo-image signal obtained as a result of the overdrive processing. Itis to be noted that the detailed configurations of the first and secondLUTs will be explained later by referring to FIGS. 3A and 3B.

The timing control section 45 is a section for controlling drivingtimings of the backlight driving section 50, the gate driver 52 and thedata driver 51 as well as a section for passing on the video-imagesignal D3 received from the overdrive processing section 44 to the datadriver 51.

In accordance with the timing control executed by the timing controlsection 45, the gate driver 52 drives pixels 20 included in theliquid-crystal display panel 2 provided along each of scan lines eachforming a row of the pixel matrix sequentially on a row-after-row basis.The scan line not shown in FIG. 1 is referred to as a gate line G to bedescribed later.

The data driver 51 is a section for supplying a video-image voltagebased on the video-image signal D3 received from the timing controlsection 45 to each of the pixels 20 employed in the liquid-crystaldisplay panel 2. To put it more concretely, the data driver 51 carriesout a D/A process of converting the digital video-image signal D3 intoan analog video-image signal which is the video-image voltage mentionedabove and outputs the analog video-image signal to the pixels 20.

The backlight driving section 51 is a section for controlling turning-onand turning-off operations of the backlight 3 in accordance with thetiming control executed by the timing control section 45.

1-1-2: Shutter Glasses 6

The viewer of the liquid-crystal display apparatus 1 wears the shutterglasses 6 in order to view a 3D image which is appearing on the displayscreen. The shutter glasses 6 are configured to include a left-eye lens6L and a right-eye lens 6R.

Each of the left-eye lens 6L and the right-eye lens 6R is provided witha light shielding shutter such as a liquid-crystal shutter which is alsonot shown in FIG. 1. The function of each of the light shieldingshutters can be put in an effective state which is defined as a closestate of the shutter or an ineffective state which is defined as an openstate of the shutter. The light shielding shutter is arbitrarilycontrolled by the control signal CTL generated by the shutter controlsection 43 to enter the close or open state. To put it more concretely,the shutter glasses 6 carry out operations to enter the close or openstate synchronously with operations carried out by the liquid-crystaldisplay apparatus 1 to switch a plurality of video images from one imageto another as will be explained later in detail.

1-1-3: Detailed Configuration of the Pixel

Next, a detailed configuration of every pixel 20 is explained byreferring to a circuit diagram of FIG. 2. FIG. 2 is a circuit diagramshowing details of a typical configuration of every pixel 20.

As shown in FIG. 2, the pixel 20 employs a liquid-crystal device 22, aTFT (Thin Film Transistor) device 21 and an auxiliary capacitor 23. Thepixel 20 is connected to a gate line G, a data line D and anauxiliary-capacitor line Cs. The gate line G is a line used forselecting the pixel 20 to serve as one of pixels to be drivensequentially. The data line D is a line used for supplying a video-imagevoltage generated by the data driver 51 on the basis of the video-imagesignal D3 to the pixel 20 serving as one of pixels to be drivensequentially.

The liquid-crystal device 22 functions as a display element for carryingout a display operation of emitting display light in accordance with thevideo-image voltage supplied to the liquid-crystal device 22 by way ofthe TFT device 21. The liquid-crystal device 22 is configured totypically include a liquid-crystal layer (not shown) and a pair ofelectrodes (not shown) which sandwich the liquid-crystal layer. Theliquid-crystal layer is configured to typically include a liquid-crystaldevice of a VA (Vertical Alignment) mode and a TN (Twisted Nematic)mode. The electrode at the specific node of the liquid-crystal device 22is connected to the drain of the TFT device 21 and a specific one of the2 nodes of the auxiliary capacitor 23. The other electrode of theliquid-crystal device 22 is connected to the ground.

The auxiliary capacitor 23 is a capacitive device for stabilizingelectric charge accumulated in the liquid-crystal device 22. Asdescribed above, the specific node of the auxiliary capacitor 23 isconnected to the drain of the TFT device 21 and the electrode at thespecific node of the liquid-crystal device 22. The other one of thenodes of the auxiliary capacitor 23 is connected to theauxiliary-capacitor line Cs.

The TFT device 21 is a MOS-FET (Metal Oxide Semiconductor-Field EffectTransistor) device. The gate of the TFT device 21 is connected to thegate line G whereas the source of the TFT device 21 is connected to thedata line D. As described above, the drain of the TFT device 21 isconnected to the specific node of the auxiliary capacitor 23 and theelectrode at the specific node of the liquid-crystal device 22. The TFTdevice 21 functions as a switching device for supplying the video-imagevoltage based on the video-image signal D3 to the specific node of theauxiliary capacitor 23 and the electrode at the specific node of theliquid-crystal device 22. To put it more concretely, the TFT device 21is put in a turned-on state selectively by a select signal supplied bythe gate driver 52 to the pixel 20 through the gate line G and connectsthe data line D to the specific node of the auxiliary capacitor 23 andthe electrode at the specific node of the liquid-crystal device 22.

1-1-4: Detailed Configurations of the LUTs for the Overdrive Processing

Next, detailed typical configurations of the first and second LUTs(Look-Up Tables) used in the overdrive processing are explained byreferring to FIGS. 3A and 3B. FIGS. 3A and 3B are model diagrams eachshowing a detailed typical configuration of an LUT used in overdriveprocessing. To put it in detail, FIG. 3A is a model diagram showing adetailed typical configuration of a first lookup table LUT1 used in anoperation to output (or write) a video-image signal to (or into) pixelsduring the first frame sub-sub-period of a frame sub-period. On theother hand, FIG. 3B is a diagram showing a detailed typicalconfiguration of a second lookup table LUT2 used in an operation tooutput (or write) the same video-image signals to (or into) pixelsduring the second frame sub-sub-period of the same frame sub-period.

Each of the first lookup tables LUT1 and LUT2 prescribes overdrivequantities, which each represent the luminance gradation of thevideo-image signal D3 obtained as a result of the overdrive processing,in accordance with the luminance gradation of the current video-imagesignal D1 and the luminance gradation of the immediately precedingvideo-image signal D2. It is to be noted that, in this case, each of theluminance gradations of the video-image signals D1, D2 and D3 has avalue in a typical range of 0 to 255. In addition, each of the firstlookup table LUT1 and the second lookup table LUT2 is shown as an LUTwhich prescribes only some representative luminance gradations. Thefollowing description also assumes such a typical range of the luminancegradations.

In the first lookup table LUT1 shown in FIG. 3A, much like the existingoverdrive processing, each of the overdrive quantities represents aluminance gradation of the video-image signal D3 and is set at such avalue that the gradation of the display luminance according to thevideo-image voltage based on the video-image signal D3 becomes equal tothe desired gradation which is used as the target gradation. To put itmore concretely, the overdrive quantities each prescribed by the firstlookup table LUT1 shown in FIG. 3A as a luminance gradation of thevideo-image signal D3 are each set at a value which makes a differencein luminance gradation between the video-image signals D2 and D3 greaterthan a difference in luminance gradation between the video-image signalsD1 and D2.

On the other hand, the second lookup table LUT2 shown in FIG. 3B is atable used for fine adjustment to sustain the display luminanceaccording to the video-image voltage based on the video-image signal D3at the desired gradation which is used as the target gradation or tochange the display luminance to the desired gradation. To put it moreconcretely, the overdrive quantities set in the second lookup table LUT2are each a quantity for sustaining a target luminance in the secondoutput/write operation carried out during the second framesub-sub-period of the same frame sub-period by performing fineadjustment such as a process of compensating for a swing-over phenomenonafter the overdrive processing carried out in the first output/writeoperation. If a target luminance gradation cannot be attained in thefirst output/write operation carried out during the first framesub-sub-period of a frame sub-period, on the other hand, an overdrivequantity set in the second lookup table LUT2 is used as an overdrivequantity for attaining the target luminance gradation in the secondoutput/write operation carried out during the second framesub-sub-period of the same frame sub-period.

1-2: Operations of the Video-Image Display System and Its Effects

Next, operations of the video-image display system and its effects areexplained.

1-2-1: Operations to Display 3D Video Images

First of all, operations carried out by the video-image display systemto display 3D video images are explained by referring to the diagrams ofFIGS. 1, 2 and 4 to 6 as follows.

1-2-2: Basic Operations

In the liquid-crystal display apparatus 1 shown in FIG. 1, thevideo-image signal processing section 41 controls the aforementionedoutput order (also referred to as a write order) of the right-eyevideo-image signal DR and the left-eye video-image signal DL for aninput video-image signal Din to generate a current video-image signal D1and supplies the video-image signal D1 to the overdrive processingsection 44. Then, the frame memory 42 is used for temporarily storing avideo-image signal D2 also based the input video-image signal Din as asignal immediately preceding the current video-image signal D1.Subsequently, in accordance with the luminance gradation of theimmediately preceding video-image signal D2 temporarily stored in theframe memory 42 and the luminance gradation of the current video-imagesignal D1 currently output by the video-image signal processing section41, the overdrive processing section 44 carries out overdrive processingon the video-image signal D1 to generate a video-image signal D3 andsupplies the video-image signal D3 to the timing control section 45.

In the mean time, the shutter control section 43 supplies a timingcontrol signal CTL to the shutter glasses 6 in accordance with timingcontrol executed by the video-image signal processing section 41.

Then, the timing control section 45 passes on the video-image signal D3to the data driver 51. Subsequently, the data driver 51 supplies avideo-image voltage based on the video-image signal D3 to each of thepixels 20. To put it more concretely, the data driver 51 carries out aD/A process of converting the digital video-image signal D3 into ananalog video-image signal which is the video-image voltage mentionedabove and outputs the analog video-image signal to the pixels 20.

Then, in accordance with the video-image voltages received by the pixels20 as driving voltages and select signals received by the pixels 20 fromthe gate driver 52, a sequential display driving operation is carriedout on each of the pixels 20 on a row-after-row basis.

To put it more concretely, as shown in FIG. 2, a select signal suppliedby the gate driver 52 to the gate of the TFT device 21 changes the stateof the TFT device 21 from a turned-off state to a turned-on state. Withthe TFT device 21 put in a turned-on state, the liquid-crystal device 22and the auxiliary capacitor 23 are connected to the data line D. As aresult, a video-image voltage based on a video-image signal D3 suppliedby the data driver 51 to the source of the TFT device 21 is applied tothe liquid-crystal device 22 in the aforementioned display drivingoperation carried out on the pixel 20 as described above.

In a pixel 20 with the liquid-crystal device 22 and the auxiliarycapacitor 23 both connected to the data line D, illuminated lightradiated by the backlight 3 to the pixel 20 is modulated and emitted bythe liquid-crystal display panel 2 as display light. Thus, theliquid-crystal display apparatus 1 displays a video image based on theinput video-image signal Din. To put it more concretely, a right-eyevideo image based on a right-eye video-image signal DR and a left-eyevideo image based on a left-eye video-image signal DL are displayedalternately on a time-division basis in the so-called time-divisiondriving operation.

During an operation shown in FIG. 4A as an operation to display a videoimage for the left eye in the time-division driving operation, a controlsignal CTL generated by the shutter control section 43 sustains thelight shielding function of the shutter of right-eye lens 6R employed inthe shutter glasses 6 used by the viewer 7 in an effective (or close)state and puts the light shielding function of the shutter of left-eyelens 6L in an ineffective (or open) state. That is to say, the left-eyelens 6L is sustained in the ineffective (or open) state for transmissionof left-eye display light LL originated from the displayed video imagefor the left eye whereas the right-eye lens 6R is sustained in theeffective (or close) state for the transmission of the left-eye displaylight LL.

During an operation shown in FIG. 4B as an operation to display a videoimage for the right eye in the time-division driving operation, on theother hand, the control signal CTL generated by the shutter controlsection 43 sustains the light shielding function of the shutter ofleft-eye lens 6L employed in the shutter glasses 6 used by the viewer 7in an effective (or close) state and puts the light shielding functionof the shutter of right-eye lens 6R in an ineffective (or open) state.That is to say, the right-eye lens 6R is sustained in the ineffective(or open) state for transmission of right-eye display light LRoriginated from the displayed video image for the right eye whereas theleft-eye lens 6L is sustained in the effective (or close) state for thetransmission of the right-eye display light LR.

The operations shown in FIGS. 4A and 4B are carried out alternately andrepeatedly so that, when the viewer 7 is looking at the display screenof the liquid-crystal display apparatus 1 by wearing the shutter glasses6, the viewer 7 sees a 3D video image. That is to say, the viewer 7 seesa video image for the left eye through the left-eye lens 6L and a videoimage for the right eye through the right-eye lens 6R. Since there is adisparity between the video image for the left eye and the video imagefor the right eye, the viewer 7 recognizes the displayed video image asa 3D video image having a depth.

1-2-3: Consecutive Write/Display Operations

FIGS. 5A and 5B are timing diagrams referred to in explanation ofcrosstalk that can be generated in an operation carried out by theexisting video-image display apparatus to display a 3D video image byadoption of such a time-division driving method. To be more specific,FIG. 5A is a timing diagram of operations to write and display a videoimage on a display screen whereas FIG. 5B is a diagram showing timingsof states of the shutter glasses 6 having the left-eye lens 6L and theright-eye lens 6R. It is to be noted that, in the timing diagram of FIG.5A, a solid-line arrow denotes an R write timing which is a timing towrite a video-image signal for the right eye. On the other hand, adashed-line arrow denotes an L write timing which is a timing to write avideo-image signal for the left eye. These solid-line and dashed-linearrows are also used in subsequent figures and mean the same things. Inthe same diagrams, a time period encircled by a dashed line is a timeperiod during which the desired display luminance of a video image forthe period is attained. For example, a time period encircled by a dashedline R0 is a time period during which the desired display luminance ofthe right-eye video image R0 output for the period is attained. Theseencircling dashed lines are also used in subsequent figures and mean thesame things.

In the timing diagram of FIG. 5B, on the other hand, a period shown in ablack color is a close-shutter period of the left-eye lens 6L and theright-eye lens 6R whereas a period shown in a white color is anopen-shutter period TonL of the left-eye lens 6L or an open-shutterperiod TonR of the right-eye lens 6R. The period shown in a black colorand the period shown in a white color are also used in subsequentfigures and mean the same things.

In the operation carried out by the existing video-image displayapparatus to display a 3D video image, as shown in the timing diagram ofFIG. 5A, in the L frame sub-period included of each frame period, asignal representing a video image for the left eye is written once intothe liquid-crystal display panel 2. Thus, left-eye video images L1, L2and so on are displayed consecutively on the liquid-crystal displaypanel 2 during a plurality of L frame sub-periods which are eachincluded in a frame period. By the same token, in the R frame sub-periodincluded in each frame period, a signal representing a video image forthe right eye is written once into the liquid-crystal display panel 2.Thus, right-eye video images R0, R1 and so on are displayedconsecutively on the liquid-crystal display panel 2 during a pluralityof R frame sub-periods which are each included in a frame period.

In the operation carried out by the existing video-image displayapparatus to display a 3D video image, it takes time for eachliquid-crystal device 22 employed in the liquid-crystal display panel 2to give a response. Thus, the time to attain the desired displayluminance lags behind the write timing. To be more specific, the time todisplay a predetermined luminance gradation of the video image for theleft eye lags behind the L write timing whereas the time to display apredetermined luminance gradation of the video image for the right eyelags behind the R write timing.

As shown in FIG. 5B, on the other hand, each of an open-shutter periodTonL of the left-eye lens 6L and an open-shutter period TonR of theright-eye lens 6R is set between the L write timing and the R writetiming.

In a liquid-crystal display apparatus adopting the time-division drivingmethod, however, video images of one frame period are displayed on thescreen sequentially on a row-after-row basis in a direction from the topof the screen to the bottom thereof as shown in the timing diagram ofFIG. 5A. Thus, without regard to how each of an open-shutter period TonLof the left-eye lens 6L and an open-shutter period TonR of the right-eyelens 6R is set between the L write timing and the R write timing, theliquid-crystal display apparatus raises the following problems.Interferences and/or crosstalk are generated between a left-eye videoimage and a right-eye video image which are adjacent to each other. Whensuch interferences and/or such crosstalk are generated, at the topand/or bottom of the display screen in the 3D image display systemmaking use of the shutter glasses 6, the right-hand side portion of adisplayed image is seen by the left eye whereas the left-hand sideportion of the displayed image is seen by the right eye or vice versa sothat the correct 3D video image can hardly be recognized. Such crosstalkand/or such interferences are generated because of poor characteristicsof the LCD apparatus and/or poor characteristics of light shieldingshutters employed in the shutter glasses 6. Poor characteristics of theLCD apparatus include an inadequate response speed of the apparatuswhereas poor characteristics of the light shielding shutters employed inthe shutter glasses 6 include insufficient shutter contrasts.

In order to solve the problems described above, the first embodiment ofthe present invention carries out operations to display a 3D video imageby adoption of a continuous write/display method like one shown in FIGS.6A and 6B. FIGS. 6A and 6B are timing diagrams referred to inexplanation of an outline of an operation carried out by the video-imagedisplay system shown in FIG. 1 to serve as an apparatus for displaying a3D video image in accordance with the first embodiment. To be morespecific, FIG. 6A is a timing diagram of operations to write video-imagesignals onto pixels and display a 3D video image whereas FIG. 6B is adiagram showing timings of states of shutter glasses 6 having a left-eyelens 6L and a right-eye lens 6R much like the timing diagrams of FIGS.5A and 5B respectively.

In the operation carried out by the video-image display system shown inFIG. 1 to display a 3D video image by adoption of the continuouswrite/display method cited above, as shown in the timing diagram of FIG.6A, in the L frame sub-period included in each frame period, a signalrepresenting a video image for the left eye is written two times in arow into the liquid-crystal display panel 2 in two consecutivewrite/display operations during first and second L frame sub-sub-periodsrespectively. Thus, two left-eye video images L1, L2 and so on aredisplayed consecutively on the liquid-crystal display panel 2 in aplurality of L frame sub-sub-periods each included in a frame period. Bythe same token, in the R frame sub-period included in each frame period,a signal representing a video image for the right eye is written twotimes in a row into the liquid-crystal display panel 2 in twoconsecutive write/display operations during first and second R framesub-sub-periods respectively. Thus, right-eye video images R0, R1 and soon are displayed consecutively on the liquid-crystal display panel 2 aplurality of R frame sub-sub-periods each included in a frame period.

That is to say, in one frame period, video images are displayed forexample in the following order: a left-eye video image L1 the left-eyevideo image L1 a right-eye video image R1 the right-eye video image R1.Then, the operation to write the video-image signal for the second timein the second write/display operation during the second framesub-sub-period is completed in the frame sub-period for the signal. In atime period during which each liquid-crystal device 22 on the entiredisplay screen is sustaining a desired luminance gradation, one of theleft-eye lens 6L and the right-eye lens 6R which are employed in theshutter glasses 6 is put in an open state. To put it more concretely, asshown in the timing diagram of FIG. 6B for example, a left-eyeopen-shutter period TonL is set between the timing to write the specificleft-eye video-image signal L1 for the second time and the timing towrite the right-eye video-image signal R1 immediately following thespecific left-eye video-image signal L1. On the other hand, a right-eyeopen-shutter period TonR is set between the timing to write theparticular right-eye video-image signal R1 for the second time and thetiming to write the left-eye video-image signal L2 immediately followingthe particular right-eye video-image signal R1.

Thus, unlike the traditional operation to display a 3D video image asshown in FIGS. 5A and 5B, in the operation to display a 3D video imageaccording to the first embodiment as shown in FIGS. 6A and 6B, ideally,the left-eye lens 6L employed in the shutter glasses 6 is put in an openstate only while a video image for the left eye is being displayed onthe entire screen whereas the right-eye lens 6R employed in the shutterglasses 6 is put in an open state only while a video image for the righteye is being displayed on the entire display screen.

1-3: Overdrive Processing

Next, with reference to diagrams of FIGS. 3 and 7 to 10 and by comparingthe first embodiment with a typical comparison example, the followingdescription explains details of the overdrive processing which serves asone of characteristics of the present invention.

First of all, the first embodiment carries out the operation to writeand display a 3D video image by adoption of a continuous write/displaymethod as described above in order to reduce the amount of crosstalk toa level lower than that provided by the existing video-image displaysystem.

During an operation to display a video image in accordance with thetime-division driving method described above, however, a plurality ofvideo images are always displayed repeatedly so that the liquid-crystaldevices 22 never get settled in a steady state in many cases. In thiscase, the video images are video images for the left and right eyes.Thus, if the overdrive processing premising a transition from the steadystate as is the case with the overdrive processing used in the existingoperation to display a 2D video image is applied as it is to avideo-image display operation carried out by adoption of thetime-division driving method in order to compensate for the insufficientresponse speed of the liquid-crystal device 22, the optimum level of anapplied voltage cannot be obtained so that a shift from target luminanceis inevitably resulted in. As a result, crosstalk is undesirablygenerated. In addition, also if the existing overdrive processing usedin the existing operation to display a 2D video image is applied as itis to a video-image display operation carried out by adoption of thecontinuous write/display method described above, similarly, a shift fromtarget luminance is resulted in unavoidably and crosstalk is undesirablygenerated as will be described as follows.

1-3-1: Overdrive Processing of a Typical Comparison Example

FIGS. 7A to 7C are timing diagrams referred to in explanation of typicaloverdrive processing provided for a comparison purpose. To put it indetail, FIGS. 7A to 7C are timing diagrams referred to in explanation ofa case in which the existing overdrive processing used in the existingoperation to display a 2D video image is applied as it is to avideo-image display operation carried out by adoption of the continuouswrite/display method according to the first embodiment as describedabove. To be more specific, FIG. 7A is a timing diagram of a currentvideo-image signal D1 whereas FIG. 7B is a timing diagram of avideo-image signal D102 which is read out from the frame memory 42. FIG.7C is a timing diagram of a video-image signal D103 which is generatedby the overdrive processing section 44.

In the timing diagrams of FIG. 7A, reference notation SFR02 denotes asecond frame sub-sub-period included in an R frame sub-period used forwriting (and displaying) a right-eye video image R0. On the other hand,reference notation SFL11 denotes a first frame sub-sub-period includedin an L frame sub-period used for writing (and displaying) a left-eyevideo image L1. By the same token, reference notation SFL12 denotes asecond frame sub-sub-period included in the L frame sub-period used forwriting (or displaying) the left-eye video image L1. On the other hand,reference notation SFR11 denotes a first frame sub-sub-period includedin an R frame sub-period used for writing (and displaying) a right-eyevideo image R1. By the same token, reference notation SFR12 denotes asecond frame sub-sub-period included in the R frame sub-period used forwriting (and displaying) the right-eye video image R1.

In addition, in the timing diagrams of FIG. 7C, reference notation “ODLUT” denotes an LUT (Look-Up Table) used in the existing OD (overdrive)processing. Reference notation L1 _(OD) denotes a left-eye video imageobtained as a result of overdrive processing carried out on the left-eyevideo image L1. By the same token, reference notation R1 _(OD) denotes aright-eye video image obtained as a result of overdrive processingcarried out on the right-eye video image R1.

It is to be noted that the reference notations described above are alsoused in subsequent diagrams and mean the same things.

In each of the consecutive write operations, the typical overdriveprocessing provided for a comparison purpose is carried out always inaccordance with the luminance gradation of the current (unitary) videoimage and the luminance gradation of an immediately preceding (unitary)video image immediately leading ahead of the current unitary video imageregardless of whether or not the current unitary video image and theimmediately preceding unitary video image are the same video image orpertain to the same video-image stream. To put it more concretely, in anL frame sub-period to write a left-eye video image L1 for example,overdrive processing like one described as follows is carried out.

First of all, in the first frame sub-sub-period SFL11, in accordancewith the luminance gradation of the video-image signal D102 alreadystored in the frame memory as a signal representing the immediatelypreceding video image R0 and the luminance gradation of the video-imagesignal D1 being processed as a signal representing the current videoimage L1, the overdrive processing is carried out in order to generate aleft-eye video image L1 _(OD). Then, in the second frame sub-sub-periodSFL12, in accordance with the luminance gradation of the video-imagesignal D102 already stored in the frame memory as a signal representingthe immediately preceding video image L1 and the luminance gradation ofthe video-image signal D1 being processed as a signal representing thecurrent video image L1, the overdrive processing is carried out. Sincethe current video image and the video image immediately preceding thecurrent video image are the same video image which is the left-eye videoimage L1 in this case, however, a difference in luminance gradationbetween the current video image and the video image immediatelypreceding the current video actually does not exist so that, virtually,no overdrive processing is carried out. Thus, a signal representing theleft-eye video image L1 is output as it is as the left-eye video-imagesignal D103. That is to say, since the overdrive processing is carriedout in only the first one of the two consecutive write operationsperformed during the first frame sub-sub-period SFL11 and the secondframe sub-sub-period SFL12 respectively, the function of the overdriveprocessing cannot be fully demonstrated.

To put it more concretely, as indicated by reference notations P101 toP103 shown in FIG. 8, in the response characteristic of the displayluminance of the liquid-crystal device 22, a big shift from a targetluminance is generated so that crosstalk undesirably occurs. The targetluminance is a gradation for a luminance ratio shown by a solid line inthe diagram of FIG. 8. It is to be noted that notation “0-64” (or thelike) used in the diagram of FIG. 8 represents a case in which aluminance-gradation difference between the gradation of 0 and thegradation of 64 is generated between the left-eye video image and theright-eye video image. To put it more concretely, notation “0-64”represents a case in which the following transitions take place:gradation of 0→gradation of 0→gradation of 64→gradation of 64→gradationof 0→gradation of 0→gradation of 64→gradation of 64→and so on. Suchnotations also mean the same things in a diagram of FIG. 10.

1-3-2: OD Processing of the First Embodiment

In the case of the first embodiment, on the other hand, overdriveprocessing described below is carried out in accordance with theluminance gradation of the immediately preceding video-image signal D2already stored in the frame memory 42 and the luminance gradation of thecurrent video-image signal D1 currently being output from thevideo-image signal processing section 41. To put it more concretely, forevery operation to output each of video-image signals included in thecurrent video-image signal D1, the overdrive processing is carried outin order to generate a video-image signal D3. The video-image signalsincluded in the current video-image signal D1 are a right-eyevideo-image signal DR and a left-eye video-image signal DL.

FIGS. 9A to 9C is a plurality of timing diagrams referred to inexplanation of the overdrive processing carried out by the firstembodiment. To be more specific, FIG. 9A is a timing diagram of thecurrent video-image signal D1, FIG. 9B is a timing diagram of theimmediately preceding video-image signal D2 whereas FIG. 9C is a timingdiagram of the newly generated video-image signal D3.

In the overdrive processing carried out by the first embodiment, anoperation to output every video-image signal included in the currentvideo-image signal D1 is carried out repeatedly two times in a rowduring first and second frame sub-sub-periods respectively, and aluminance gradation of the immediately preceding video-image signal D2other than and different from the current video-image signal D1 is usedin the overdrive processing as a gradation common to the overdriveprocessing carried out during the first frame sub-sub-period and theoverdrive processing carried out during the second frame sub-sub-period.As described above, the video-image signals included in the currentvideo-image signal D1 are a right-eye video-image signal DR and aleft-eye video-image signal DL. The overdrive processing can be carriedout by making use of the luminance gradation of the immediatelypreceding video-image signal D2 because, during the current framesub-period, the immediately preceding video-image signal D2 output bythe video-image signal processing section 41 in the immediatelypreceding frame sub-period has been always stored in the frame memory 42as explained earlier. The current frame sub-period can be an L framesub-period or an R frame sub-period.

Thus, if the current frame sub-period is an L frame sub-period forexample, in the overdrive processing carried out by the overdriveprocessing section 44, an operation to output a left-eye video-imagesignal DL serving as the current video-image signal D1 is carried outrepeatedly two times in a row during respectively the first and secondframe sub-sub-periods of the current L frame sub-period, and a luminancegradation of a right-eye video-image signal DR output in an R framesub-period immediately preceding the current L frame sub-period to serveas the immediately preceding video-image signal D2 is used in theoverdrive processing as a gradation common to the overdrive processingcarried out during the first frame sub-sub-period and the overdriveprocessing carried out during the second frame sub-sub-period. To put itmore concretely, in the current L frame sub-period to write a left-eyevideo-image signal L1 for example, overdrive processing like onedescribed as follows is carried out.

First of all, in the first frame sub-sub-period SFL11, overdriveprocessing is carried out in order to generate a left-eye video image L1_(OD1) in accordance with the luminance gradation of the video-imagesignal D2 already stored in the frame memory 42 as a signal representingthe video image R0 output during an R frame sub-period immediatelypreceding the current L frame sub-period and the luminance gradation ofthe video-image signal D1 currently being processed as a signalrepresenting the current video image L1.

Then, in the same way as the first frame sub-sub-period SFL11, in thesecond frame sub-sub-period SFL12, overdrive processing is carried outin order to generate a left-eye video image L1 _(OD2) in accordance withthe luminance gradation of the video-image signal D2 already stored inthe frame memory 42 as a signal representing the video image R0 outputduring an R frame sub-period immediately preceding the current L framesub-period and the luminance gradation of the video-image signal D1currently being processed as a signal representing the current videoimage L1.

That is to say, the overdrive processing according to the firstembodiment is different from the overdrive processing described beforeas the typical overdrive processing provided for a comparison purpose inthat, in the case of the overdrive processing according to the firstembodiment, it is possible to avoid a case in which, also for the secondframe sub-sub-period SFL12, the current video image and an immediatelypreceding video image immediately leading ahead of the current videoimage are inadvertently the same video image. Thus, in the case of theoverdrive processing according to the first embodiment, it is possibleto prevent overdrive processing from being carried out without adifference in luminance gradation between the current video image andthe immediately preceding video image immediately leading ahead of thecurrent video image.

If the current frame sub-period is an R frame sub-period, on the otherhand, in the overdrive processing carried out, an operation to output aright-eye video-image signal DR serving as the current video-imagesignal D1 is carried out repeatedly two times in a row duringrespectively the first and second frame sub-sub-periods of the current Rframe sub-period, and a luminance gradation of a left-eye video-imagesignal DL output in an L frame sub-period immediately preceding thecurrent R frame sub-period to serve as the immediately precedingvideo-image signal D2 is used in the overdrive processing as a gradationcommon to the overdrive processing carried out during the first framesub-sub-period and the overdrive processing carried out during thesecond frame sub-sub-period. To put it more concretely, in the current Rframe sub-period to write a right-eye video-image signal R1 for example,overdrive processing like one described as follows is carried out.

First of all, in the first frame sub-sub-period SFR11, overdriveprocessing is carried out in order to generate a right-eye video imageR1 _(OD1) in accordance with the luminance gradation of the video-imagesignal D2 already stored in the frame memory 42 as a signal representingthe video image L1 output during an L frame sub-period immediatelypreceding the current R frame sub-period and the luminance gradation ofthe video-image signal D1 currently being processed as a signalrepresenting the current video image R1.

Then, in the same way as the first frame sub-sub-period SFR11, in thesecond frame sub-sub-period SFR12, overdrive processing is carried outin order to generate a right-eye video image R1 _(OD2) in accordancewith the luminance gradation of the video-image signal D2 already storedin the frame memory 42 as a signal representing the video image L1output during an L frame sub-period immediately preceding the current Rframe sub-period and the luminance gradation of the video-image signalD1 currently being processed as a signal representing the current videoimage R1.

That is to say, the overdrive processing according to the firstembodiment is different from the overdrive processing described beforeas the typical overdrive processing provided for a comparison purpose inthat, in the case of the overdrive processing according to the firstembodiment, it is possible to avoid a case in which, also for the secondframe sub-sub-period SFR12, the current video image and an immediatelypreceding video image immediately leading ahead of the current videoimage are inadvertently the same video image. Thus, in the case of theoverdrive processing according to the first embodiment, it is possibleto prevent overdrive processing from being carried out without adifference in luminance gradation between the current video image andthe immediately preceding video image immediately leading ahead of thecurrent video image.

In the overdrive processing carried out by the overdrive processingsection 44 in accordance with the first embodiment, an operation tooutput every video-image signal included in the current video-imagesignal D1 is performed repeatedly two times in a row during first andsecond frame sub-sub-periods respectively. A LUT (Look-Up Table)prescribing overdrive quantities is referred to in each of the twoconsecutive output/write operations carried out during the first andsecond frame sub-sub-periods respectively. However, a first lookup tableLUT1 used in the first one of the two consecutive output/writeoperations is different from a second lookup table LUT2 used in thesecond one. The overdrive quantities prescribed by the first lookuptable LUT1 used in the first output/write operation are different fromthe overdrive quantities prescribed by the second lookup table LUT2 usedin the second output/write operation. One of the overdrive quantitiesprescribed by the first lookup table LUT1 or the second lookup tableLUT2 is selected in accordance with the luminance gradation of thecurrent video-image signal D1 and the luminance gradation of theimmediately preceding video-image signal D2. The selected overdrivequantity is used as the luminance gradation of the video-image signal D3newly generated in the overdrive processing.

A typical example of the first lookup table LUT1 used in the firstoutput/write operation corresponding to for example the first framesub-sub-period SFL11 or SFR11 described before is a first lookup tableLUT1 shown in FIG. 3A. In the first lookup table LUT1, much like theexisting overdrive processing, each of the overdrive quantitiesrepresents a luminance gradation of the video-image signal D3 and is setat such a value that the gradation of the display luminance according tothe video-image voltage based on the video-image signal D3 becomes equalto the desired gradation which is used as the target gradation. To putit more concretely, the overdrive quantities each prescribed by thefirst lookup table LUT1 as a luminance gradation of the video-imagesignal D3 are each set at a value which makes a difference in luminancegradation between the video-image signals D2 and D3 greater than adifference in luminance gradation between the video-image signals D1 andD2. Thus, in the same way as the existing overdrive processing, theresponse speed of each liquid-crystal device 22 can be increased.

On the other hand, a second lookup table LUT2 shown in FIG. 3B is atable used in the second output/write operation carried out during forexample the second frame sub-sub-period SFL12 or SFR12 described before.The second lookup table LUT2 shown in FIG. 3B is a table used for fineadjustment to sustain the display luminance according to the video-imagevoltage based on the video-image signal D3 at the desired gradationwhich is used as the target gradation, or to change the displayluminance to the desired gradation. To put it more concretely, theoverdrive quantities set in the second lookup table LUT2 are each aquantity for sustaining a target luminance in the second output/writeoperation carried out during the second frame sub-sub-period of the sameframe sub-period by performing fine adjustment such as a process ofcompensating for a swing-over phenomenon after the overdrive processingassociated with the first output/write operation. If a target luminancegradation cannot be attained in the first output/write operation, on theother hand, an overdrive quantity set in the second lookup table LUT2 isused as an overdrive quantity for attaining a target luminance gradationin the second output/write operation. Thus, unlike the typical overdriveprocessing provided for a comparison purpose, in the second output/writeoperation, the target luminance can be sustained.

As described above, in the overdrive processing carried out by the firstembodiment, an operation to output every video-image signal included inthe current video-image signal D1 (a right-eye video-image signal DR anda left-eye video-image signal DL) is carried out repeatedly two times,and a luminance gradation of a video-image signal output in a framesub-period immediately preceding the current frame sub-period to serveas the immediately preceding video-image signal D2 is used in theoverdrive processing as a gradation common to the overdrive processingcarried out during the first frame sub-sub-period and the overdriveprocessing carried out during the second frame sub-sub-period.

On the other hand, the typical overdrive processing provided for acomparison purpose is carried out in each of the consecutiveoutput/write operations always in accordance with the luminancegradation of the current (unitary) video image and the luminancegradation of an immediately preceding (unitary) video image immediatelyleading ahead of the current unitary video image regardless of whetheror not the current unitary video image and the immediately precedingunitary video image immediately are the same video image or pertain tothe same video-image stream.

Thus, in comparison with the typical overdrive processing provided for acomparison purpose, it is possible to reduce a shift between the targetluminance and the display luminance based on the video-image signal D3which is obtained as a result of the overdrive processing carried out bythe first embodiment. The display luminance based on the video-imagesignal D3 is used as the display luminance of the liquid-crystal device22.

To put it more concretely, as indicated by reference notations P1, P2and P3 shown in FIG. 10, in the response characteristic of the displayluminance generated by the liquid-crystal device 22 in accordance with avideo-image voltage applied to the pixel 20 employing the liquid-crystaldevice 22, the shift from the target luminance is reduced to a valuesmaller than the shift generated in the typical overdrive processing asshown in FIG. 8. Thus, in comparison with the typical overdriveprocessing, it is possible to reduce the amount of crosstalk whichappears as interferences among a plurality of consecutive video images.

In the first embodiment described so far, an immediately precedingunitary video image D2 immediately leading ahead of a current unitaryvideo image D1 currently output by the video-image signal processingsection 41 is stored as it is in the frame memory 42. The currentunitary video image D1 pertains to a current video-image stream whereasthe immediately preceding video image D2 is selected from an immediatelyvideo-image stream which is other than and different from the currentvideo-image stream. Each of the current video-image stream and theimmediately preceding video-image stream includes a left-eye video-imagesignal DL and a right-eye video-image signal DR. In addition, inaccordance with the luminance gradation of the immediately precedingvideo-image signal D2 already stored in the frame memory 42 and theluminance gradation of the current video-image signal D1 presently beingoutput by the video-image signal processing section 41, the overdriveprocessing section 44 carries out overdrive processing on the currentvideo-image signal D1 in order to generate a video-image signal D3.

On the other hand, the typical overdrive processing provided for acomparison purpose is carried out in each of the consecutive writeoperations always in accordance with the luminance gradation of thecurrent (unitary) video image and the luminance gradation of animmediately preceding (unitary) video image immediately leading ahead ofthe current unitary video image regardless of whether or not the currentunitary video image and the immediately preceding unitary video imageare the same (unitary) video image or pertain to the same video-imagestream.

Thus, in comparison with the typical overdrive processing provided for acomparison purpose, it is possible to reduce a shift between the targetluminance and the display luminance based on the video-image signal D3which is obtained as a result of the overdrive processing carried out bythe first embodiment. The display luminance based on the video-imagesignal D3 is used as the display luminance of the liquid-crystal device22. As a result, it is possible to reduce the amount of crosstalk whichappears as interferences among a plurality of consecutive video images.

In addition, in the overdrive processing carried out by the overdriveprocessing section 44 in accordance with the first embodiment, anoperation to output every video-image signal is performed repeatedly twotimes in a row in first and second output/write operations respectivelyduring the first and second frame sub-sub-periods of a frame sub-period.The lookup table LUT1 used in the overdrive processing carried outduring the first frame sub-sub-period is different from the lookup tableLUT2 used in the overdrive processing carried out during the secondframe sub-sub-period. The overdrive quantities set in the second lookuptable LUT2 as overdrive quantities of the video-image signal D3 are eacha quantity used for fine adjustment of sustaining a target luminance inthe second output/write operation carried out during the second framesub-sub-period of the same frame sub-period by performing the fineadjustment such as a process of compensating for a swing-over phenomenonafter the overdrive processing associated with the first output/writeoperation. Thus, unlike the typical overdrive processing provided for acomparison purpose, in the second output/write operation carried outduring the second frame sub-sub-period, the target luminance can besustained. As a result, in a period during which the target luminancehas been sustained throughout the entire display screen, the shutterscan be put in an open state so that it is possible to reduce the amountof crosstalk.

2: Second Embodiment

Next, a second embodiment of the present invention is explained. It isto be noted that components employed in the second embodiment to serveas components identical with their respective counterparts included inthe first embodiment are denoted by the same reference numerals or thesame reference notations as the counterparts. In addition, the identicalcomponents are not explained again in order to avoid duplications ofexplanations unless descriptions of the identical components areabsolutely required.

FIGS. 11A to 11C are timing diagrams referred to in explanation ofoverdrive processing carried out by the second embodiment of the presentinvention. To be more specific, FIG. 11A is a timing diagram of acurrent video-image signal D1, FIG. 11B is a timing diagram of animmediately preceding video-image signal D2 whereas FIG. 14C is a timingdiagram of a newly generated video-image signal D3.

In the same way as the first embodiment, the overdrive processing iscarried out by the second embodiment on the current video-image signalD1, which is output by the video-image signal processing section 41 fromthe input video-image signal Din, and an immediately precedingvideo-image signal D2 already stored in the frame memory 42 in order togenerate the video-image signal D3 as a result of the overdriveprocessing. In the case of the second embodiment, however, theimmediately preceding video-image signal D2 stored in the frame memory42 has an updated luminance gradation. That is to say, before theimmediately preceding video-image signal D2 is stored in the framememory 42, the luminance gradation of the immediately precedingvideo-image signal D2 is updated by referring to a replacement-value LUT(lookup table) to be described later in order to generate apost-replacement video-image signal D2. Then, the video-image signalprocessing section 41 newly stores the post-replacement video-imagesignal D2 in the frame memory 42.

To put it more concretely, for example, in a second frame sub-sub-periodSFR02 explained earlier, as shown in FIGS. 11A to 11C, the video-imagesignal processing section 41 makes use of the replacement-value LUT toreplace the luminance gradation of the video-image signal D1 (or, to bemore specific, the right-eye video-image signal R0) serving as theimmediately preceding video-image signal D2 to be newly stored in theframe memory 42 in order to generate a video-image signal D2 (or, to bemore specific, the right-eye video-image signal R0′) which is thepost-replacement video-image signal D2 cited above. Then, thevideo-image signal processing section 41 stores the post-replacementvideo-image signal D2 in the frame memory 42 as the immediatelypreceding video-image signal D2.

By the same token, in another second frame sub-sub-period SFL12explained earlier, as shown in FIGS. 11A to 11C, the video-image signalprocessing section 41 makes use of the replacement-value LUT to replacethe luminance gradation of the video-image signal D1 (or, to be morespecific, the left-eye video-image signal L1) serving as the immediatelypreceding video-image signal D2 to be newly stored in the frame memory42 in order to generate a video-image signal D2 (or, to be morespecific, the left-eye video-image signal L1′) which is thepost-replacement video-image signal D2 cited above. Then, thevideo-image signal processing section 41 stores the post-replacementvideo-image signal D2 in the frame memory 42.

In the same way, in a further second frame sub-sub-period SFR12explained earlier, as shown in FIGS. 11A to 11C, the video-image signalprocessing section 41 makes use of the replacement-value LUT to replacethe luminance gradation of the video-image signal D1 (or, to be morespecific, the right-eye video-image signal R1) serving as theimmediately preceding video-image signal D2 to be newly stored in theframe memory 42 in order to generate a video-image signal D2 (or, to bemore specific, the right-eye video-image signal R1′) which is thepost-replacement video-image signal D2 cited above. Then, thevideo-image signal processing section 41 stores the post-replacementvideo-image signal D2 in the frame memory 42.

FIG. 12 is a diagram showing a typical replacement-value lookup tableLUT0 used in the second embodiment to replace the luminance gradation ofthe immediately preceding video-image signal D2 before the immediatelypreceding video-image signal D2 is stored in the frame memory 42. In thetable shown in FIG. 12, for the sake of clarity, reference notation D1denotes the new immediately preceding video-image signal D2 to be newlystored in the frame memory 42, reference notation D2 at the top denotesthe immediately preceding video-image signal D2 stored so far in theframe memory 42 whereas reference notation D2 on the right side denotesthe new immediately preceding video-image signal D2 having its luminancegradation already replaced with a new one. Thus, reference notation D1used in the descriptions of the second embodiment and a second modifiedversion to be explained later denotes a new immediately precedingvideo-image signal D2 to be newly stored in the frame memory 42.

That is to say, the luminance gradations on the leftmost column of thereplacement-value lookup table LUT0 shown in FIG. 12 are the luminancegradations of the immediately preceding video-image signal D2 to benewly stored in the frame memory 42 whereas the luminance gradations onthe uppermost row of the replacement-value lookup table LUT0 are theoriginal (pre-replacement) luminance gradations of the immediatelypreceding video-image signal D2 stored so far in the frame memory 42.The replacement-value lookup table LUT0 prescribes replacement valuesfor different original (pre-replacement) luminance gradations of thepre-replacement video-image signal D2 to be newly stored in the framememory and different luminance gradations of the immediately precedingvideo-image signal D2 stored so far in the frame memory 42. Each of thereplacement values prescribed by the replacement-value lookup table LUT0is used as a luminance gradation for replacing the luminance gradationof the immediately preceding video-image signal D2 in the process toreplace a luminance gradation so as to generate a post-replacementvideo-image signal D2 having the replacement value as the luminancegradation thereof. The post-replacement video-image signal D2 having thereplacement value as the luminance gradation thereof is then stored inthe frame memory 42 to replace the pre-replacement video-image signal D2which has been existing in the frame memory 42 so far.

It is to be noted that the luminance gradation of each of theimmediately preceding video-image signal D2 stored so far in the framememory 42 and the post-replacement video-image signal D2 newly stored inthe frame memory 42 has a value in a typical range of 0 to 255. Inaddition, the replacement-value lookup table LUT0 is shown as an LUTwhich prescribes only some representative replacement values each usedas a replacement gradation. The following description also assumes sucha typical range of the luminance gradations and the fact that thereplacement-value lookup table LUT0 prescribes only some representativeluminance gradations.

In addition, in order to make the replacement-value lookup table LUT0compatible with gradation transitions in a range determined in advance,each of the replacement values is set at a selected value in thereplacement-value lookup table LUT0. In this case, a first gradationtransition in the range determined in advance is a transition from ahigh luminance gradation of the pre-replacement video-image signal D2stored in the frame memory 42 so far to a low luminance gradation of thepost-replacement video-image signal D2 to be newly stored in the framememory whereas a second gradation transition in the range determined inadvance is a transition from a low luminance gradation of thepre-replacement video-image signal D2 stored in the frame memory 42 sofar to a medium luminance gradation of the post-replacement video-imagesignal D2 to be newly stored in the frame memory. The pre-replacementvideo-image signal D2 to be newly stored in the frame memory is denotedby reference notation D1 in the replacement-value lookup table LUT0shown in FIG. 12.

FIG. 13 is a diagram showing a typical response characteristic of thedisplay luminance in the course of execution of the overdrive processingshown in FIGS. 11A to 11C. The display luminance is the luminanceexhibited by the liquid-crystal device 22 due to application of avideo-image voltage to the pixel 20 employing the liquid-crystal device22. A dotted-line curve shown in FIG. 13 for a purpose of comparisonrepresents overdrive processing according to the first embodiment inwhich the luminance gradation of the immediately preceding video-imagesignal D2 is not replaced with a replacement value before theimmediately preceding video-image signal D2 is stored in the framememory 42. On the other hand, a solid-line curve in the diagram of FIG.13 represents overdrive processing according to the second embodiment inwhich the luminance gradation of the immediately preceding video-imagesignal D2 is replaced with a replacement value before the immediatelypreceding video-image signal D2 is stored in the frame memory 42.

For the curves shown in FIG. 13, each of the right-eye video-imagesignal DR and the left-eye video-image signal DL which are included inthe current video-image signal D1 is written two times in a row in twoconsecutive write operations during two successive frame sub-sub-periodsrespectively. In each of the two consecutive operations to write each ofthe right-eye video-image signal DR and the left-eye video-image signalDL, the display-luminance gradation makes the following transitions:gradation of 255→gradation of 255→gradation of 0→gradation of0→gradation of 128→gradation of 128→gradation of 255→gradation of 255.Each number enclosed in parentheses shown in the diagrams of FIGS. 11Ato 11C and FIG. 13 is the value of a luminance gradation.

In the case of the overdrive processing carried out without replacingthe luminance gradation of the immediately preceding video-image signalD2 before the immediately preceding video-image signal D2 is stored inthe frame memory 42, each of gradation transitions from a gradation of255 in the second frame sub-sub-period SFR02 to a gradation of 0 in thefirst and second frame sub-sub-periods SFL11 and SFL12 is a transitionfrom a high gradation to a low gradation. Thus, the state of theliquid-crystal device 22 cannot completely attain the gradation of 0after each of the transitions. Then, in each of subsequent gradationtransitions from a gradation of 0 in the first and second framesub-sub-periods SFL11 and SFL12 to a gradation of 128 in the first andsecond frame sub-sub-periods SFR11 and SFR12, in the case of theoverdrive processing without replacing the luminance gradation of theimmediately preceding video-image signal D2 before the immediatelypreceding video-image signal D2 is stored in the frame memory 42,excessive overdrive processing for each of the gradation transitionsfrom a gradation of 0 to a gradation of 128 is carried out. Thus, asindicated by the dotted-line curve shown in FIG. 13 to represent theresponse characteristic of the display luminance, a shift from thetarget luminance which is the gradation of 128 in this case is left to acertain degree as before.

In the case of the overdrive processing carried out by replacing theluminance gradation of the immediately preceding video-image signal D2before the immediately preceding video-image signal D2 is stored in theframe memory 42, on the other hand, as indicated by reference notationP4 shown in FIG. 12 and as shown in FIGS. 11A to 11C, in each of thegradation transitions from a gradation of 0 in the first and secondframe sub-sub-periods SFL11 and SFL12 to a gradation of 128 in the firstand second frame sub-sub-periods SFR11 and SFR12, a process to replacethe luminance gradation of a new immediately preceding video-imagesignal D2 before the new immediately preceding video-image signal D2 isstored in the frame memory 42 is carried out on the basis of thereplacement luminance gradation of an old immediately precedingvideo-image signal D2 already stored in the frame memory 42 and thereplacement luminance gradation of the new immediately precedingvideo-image signal D2 to be newly stored in the frame memory 42 asfollows. In the table shown in FIG. 12, for the sake of clarity,reference notation D1 denotes the new immediately preceding video-imagesignal D2 to be newly stored in the frame memory 42, reference notationD2 at the top denotes the old immediately preceding video-image signalD2 stored so far in the frame memory 42 whereas reference notation D2 onthe right side denotes the new immediately preceding video-image signalD2 having its luminance gradation already replaced with a new one. Thus,reference notation D1 used in the descriptions of the second embodimentand a second modified version to be explained later denotes a newimmediately preceding video-image signal D2 to be newly stored in theframe memory 42. The video-image signal processing section 41 changesthe luminance gradation of the current video-image signal D1 (or, to bemore specific, a left-eye video image L1 of the current video-imagesignal D1) from a gradation of 0 to a gradation of 28 in order togenerate a post-replacement video-image signal D2 (or, to be specific, aleft-eye video image L1′ of the video-image signal D2). Then, thevideo-image signal processing section 41 stores the left-eye video imageL1′ of the video-image signal D2 in the frame memory 42. Thus, in thegradation transition from a gradation of 0 to a gradation of 128, theoverdrive processing section carries out overdrive processingcorresponding to a transition of the luminance gradation to thegradation of 128 from the gradation of 28 instead of the gradation of 0.That is to say, the overdrive quantity is small in comparison with theoverdrive processing carried out without replacing the luminancegradation of the immediately preceding video-image signal D2. As aresult, as indicated by an arrow shown in FIG. 13, in the solid-linecurve shown in FIG. 13 to represent the response characteristic of thedisplay luminance, a shift from the target luminance which is thegradation of 128 in this case is small in comparison with the overdriveprocessing carried out without replacing the luminance gradation of theimmediately preceding video-image signal D2. In addition, the scales ofphenomena such as excessive compensation and tail dragging which occurin the operation to display a video image are small in comparison withthe overdrive processing carried out without replacing the luminancegradation of the immediately preceding video-image signal D2.

As described above, in the case of the second embodiment, thevideo-image signal processing section 41 makes use of thereplacement-value lookup table LUT0 shown in FIG. 12 in order to replacethe luminance gradation of the input video-image signal Din handled asthe video-image signal D1 with a replacement luminance gradation and theluminance gradation of the pre-replacement video-image signal D2. Then,the video-image signal processing section 41 stores a video-image signalhaving the replacement luminance gradation in the frame memory 42. Thus,in overdrive processing corresponding to a transition in theaforementioned range determined in advance, excessive overdriveprocessing can be avoided. As a result, it is possible to reduce thescales of the phenomena such as excessive compensation and tail draggingwhich occur in the operation to display a video image by adoption of thetime-division driving method. In addition, the quality of a displayedmoving image can be improved.

To put it more concretely, in order to make the replacement-value lookuptable LUT0 compatible with gradation transitions in a range determinedin advance, each of the replacement values is set at a selected value inthe replacement-value lookup table LUT0. In this case, a first gradationtransition in the range determined in advance is a transition from ahigh luminance gradation of the pre-replacement video-image signal D2stored so far in the frame memory 42 to a low luminance gradation of thevideo-image signal D1 serving as the post-replacement video-image signalD2 to be newly stored in the frame memory whereas a second gradationtransition in the range determined in advance is a transition from a lowluminance gradation of the pre-replacement video-image signal D2 storedso far in the frame memory 42 to a medium luminance gradation of thevideo-image signal D1 serving as the post-replacement video-image signalD2 to be newly stored in the frame memory.

3: Modified Versions

Next, some modified versions of the present invention are explained. Itis to be noted that components employed in each of the modified versionsto serve as components identical with their respective counterpartsincluded in the first and second embodiments are denoted by the samereference numerals or the same reference notations as the counterparts.In addition, the identical components are not explained again in orderto avoid duplications of explanations unless descriptions of theidentical components are absolutely required.

3-1: First and Second Modified Versions

FIGS. 14A to 14C are timing diagrams referred to in explanation ofoverdrive processing carried out by a first modified version of thepresent invention. To be more specific, FIG. 14A is a timing diagram ofa current video-image signal D1, FIG. 14B is a timing diagram of animmediately preceding video-image signal D2 whereas FIG. 14C is a timingdiagram of a newly generated video-image signal D3.

On the other hand, FIGS. 15A to 15C are timing diagrams referred to inexplanation of overdrive processing carried out by a second modifiedversion of the present invention. To be more specific, FIG. 15A is atiming diagram of a current video-image signal D1, FIG. 15B is a timingdiagram of an immediately preceding video-image signal D2 whereas FIG.15C is a timing diagram of a newly generated video-image signal D3.

It is to be noted that the first modified version to be explained byreferring to FIGS. 14A to 14C is obtained by modifying the firstembodiment whereas the second modified version to be explained byreferring to FIGS. 15A to 15C is obtained by modifying the secondembodiment.

As shown in FIGS. 14A to 14C and FIGS. 15A to 15C, in each of the firstand second modified versions, during the L frame sub-period of eachframe period, a left-eye video-image signal is written into theliquid-crystal display panel 2 three times in a row in three consecutivewrite operations during three consecutive frame sub-sub-periodsrespectively in order to display left-eye video images L1, L2 and so on.By the same token, during the R frame sub-period of each frame period, aright-eye video-image signal is written into the liquid-crystal displaypanel 2 three times in a row in three consecutive write operationsduring three consecutive frame sub-sub-periods respectively in order todisplay right-eye video images R0, R1 and so on. That is to say, in oneframe period, for example, video images are consecutively displayed onthe liquid-crystal display panel 2 in the following order: left-eyevideo image L1→left-eye video image L1→left-eye video image L1→right-eyevideo image R1→right-eye video image R1→right-eye video image R1. Then,after the third one of the three consecutive write operations to writethe left-eye video image L1 at the end of the L frame sub-period iscompleted and the liquid-crystal device 22 has responded sufficiently tothe third write operation, the left-eye lens 6L employed in the shutterglasses 6 put in an open state. By the same token, after the third oneof the three consecutive write operations to write the right-eye videoimage R1 at the end of the R frame sub-period is completed and theliquid-crystal device 22 has responded sufficiently to the third writeoperation, the right-eye lens 6R employed in the shutter glasses 6 putin an open state.

In each of the first and second modified versions, if the current framesub-period is an L frame sub-period for example, overdrive processing iscarried out by making use of the luminance gradation of the right-eyevideo signal DR appearing in an R frame sub-period immediately leadingahead of the current L frame sub-period as a luminance gradation commonto the three consecutive write operations carried out during the currentL frame sub-period. By the same token, if the current frame sub-periodis an R frame sub-period, on the other hand, overdrive processing iscarried out by making use of the luminance gradation of the left-eyevideo signal DL appearing in an L frame sub-period immediately leadingahead of the current R frame sub-period as a luminance gradation commonto the three consecutive write operations carried out during the currentR frame sub-period.

The overdrive processing cited above is carried out in the overdriveprocessing section 44 by making use of three different lookup tables ODLUT1 to OD LUT3 each shown in the diagrams of FIGS. 14A to 14C and FIGS.15A to 15C to serve as a lookup table used for prescribing overdrivequantities. To be more specific, in the first one of the threeconsecutive frame sub-sub-periods to output (write) a particularvideo-image signal included in the current video-image signal D1, theoverdrive processing is carried out by making use of the first lookuptable OD LUT1 in order to generate a video-image signal D3 such an L1_(OD1) shown in each of the diagrams of FIGS. 14A to 14C and FIGS. 15Ato 15C. In the second one of the three consecutive frame sub-sub-periodsto output (write) the same particular video-image signal, the overdriveprocessing is carried out by making use of the second lookup table ODLUT2 used for prescribing overdrive quantities different from overdrivequantities prescribed by the first lookup table OD LUT1 in order togenerate a video-image signal D3 such an L1 _(OD2) shown in FIGS. 14A to14C and FIGS. 15A to 15C. In the third one of the three consecutiveframe sub-sub-periods to output (write) the same particular video-imagesignal, the overdrive processing is carried out by making use of thethird lookup table OD LUT3 used for prescribing overdrive quantitiesdifferent from overdrive quantities prescribed by the first lookup tableOD LUT1 and different from overdrive quantities prescribed by the secondlookup table OD LUT2 in order to generate a video-image signal D3 suchan L1 _(OD3) shown in FIGS. 14A to 14C and FIGS. 15A to 15C.

It is to be noted that the third lookup table OD LUT3 used in the thirdone of the three consecutive frame sub-sub-periods to output or writethe same particular video-image signal is a lookup table for fineadjustment such as a process of compensating for a swing-over phenomenonas is the case with the second lookup table LUT2 shown in FIG. 3B toserve as a lookup table used in a second frame sub-sub-period in thecase of the first embodiment.

In the second modified version explained below by referring to FIGS. 15Ato 15C, in the same way as the second embodiment, the video-image signalprocessing section 41 replaces the luminance gradation of thevideo-image signal D1 with a replacement value in order to generate apost-replacement video-image signal D2 having the replacement value asthe luminance gradation thereof. Then, the video-image signal processingsection 41 stores the post-replacement video-image signal D2 in theframe memory 42. To put it more concretely, for example, in a thirdframe sub-sub-period SFR03, the video-image signal processing section 41refers to the replacement-value lookup table LUT to find a replacementvalue to be used for replacing the luminance gradation of the right-eyevideo-image signal R0 of a video-image signal D1 in order to generate aright-eye video image R0′ which serves as the post-replacementvideo-image signal D2. Then, the video-image signal processing section41 stores the post-replacement video-image signal D2 in the frame memory42. By the same token, in a third frame sub-sub-period SFL13, thevideo-image signal processing section 41 refers to the replacement-valuelookup table LUT to find a replacement value to be used for replacingthe luminance gradation of the left-eye video-image signal L1 of avideo-image signal D1 in order to generate a left-eye video image L1′which serves as the post-replacement video-image signal D2. Then, thevideo-image signal processing section 41 stores the post-replacementvideo-image signal D2 in the frame memory 42.

As described above, the first and second modified versions carry outoperations similar to those carried out by the first and secondembodiments respectively in order to produce the same effects. That isto say, during one of frame sub-periods of each frame period, avideo-image signal may be written into the liquid-crystal display panel2 three times in a row in at least three consecutive framesub-sub-periods in order to display video images represented by thevideo-image signal. Even in such a configuration, it is possible toproduce the same effects as those as the first and second embodiments.

3-2: Third Modified Version

FIGS. 16A and 16B are model diagrams each referred to in explanation ofan outline of an operation carried out by a video-image display systemaccording to a third modified version of the present invention todisplay a 3D video image. The video-image display system according tothe third modified version is referred to as a multi-view system.

The third modified version implements a video-image display system whichis capable of carrying out a multi-image display operation in place ofthe 3D image display operation carried out by the first and secondembodiments as well as the first and second modified versions asexplained so far. In the multi-image display operation, a plurality ofvideo images different from each other are displayed individually to aplurality of viewers which are each also referred to as a user. In thecase of the third modified version, two video images different from eachother are displayed individually to two viewers respectively.

In the multi-view system according to the third modified version, afirst video image based on a first video-image signal for the firstviewer and a second video image based on a second video-image signal forthe second viewer are displayed alternately on a time-division basis. Inthe case of the first and second embodiments, as explained so far, aleft-eye video image is displayed to the right-eye lens 6R employed inthe shutter glasses 6 whereas a left-eye video image is displayed to theright-eye lens 6R and the video images are alternately on atime-division basis. In the case of the multi-view system according tothe third modified version, on the other hand, first and second videoimages for first and second viewers respectively are displayedalternately on a time-division basis.

To put it more concretely, as shown in FIG. 16A, a first control signalCTL1 sustains the light shielding functions of both the left-eye lens 6Land the right-eye lens 6R which are employed in first shutter glasses 61worn by a first viewer 71 in an ineffective state while the first 3Dvideo image V1 is being displayed. On the other hand, a second controlsignal CTL2 sustains the light shielding functions of both the left-eyelens 6L and the right-eye lens 6R which are employed in second shutterglasses 62 worn by a second viewer 72 in an effective state while thefirst 3D video image V1 is being displayed. That is to say, the firstshutter glasses 61 worn by the first viewer 71 are put in a state ofbeing open to transmission of display light LV1 which emanates from thedisplayed first 3D video image V1. On the other hand, the second shutterglasses 62 worn by the second viewer 72 are put in a state of beingclose to the transmission of the display light LV1.

As shown in FIG. 16B, on the other hand, a first control signal CTL1sustains the light shielding functions of both the left-eye lens 6L andthe right-eye lens 6R which are employed in first shutter glasses 61worn by the first viewer 71 in an effective state while the second 3Dvideo image V2 is being displayed. On the other hand, a second controlsignal CTL2 sustains the light shielding functions of both the left-eyelens 6L and the right-eye lens 6R which are employed in second shutterglasses 62 worn by the second viewer 72 in an ineffective state whilethe first 3D video image V2 is being displayed. That is to say, thefirst shutter glasses 61 worn by the first viewer 71 are put in a stateof being close to transmission of display light LV2 which emanates fromthe displayed first 3D video image V2. On the other hand, the secondshutter glasses 62 worn by the second viewer 72 are put in a state ofbeing open to the transmission of the display light LV2.

The state shown in FIG. 16A and the state shown in FIG. 16B areestablished repeatedly as well as alternately on a time-division basisso that the first 3D video image V1 and the second 3D video image V2which are different from each other are displayed individually to thetwo viewers 71 and 72 respectively in the so-called multi-view mode.

It is also possible to apply the OD processing explained in thedescriptions of the first and second embodiments as well as the firstand second modified versions to the multi-image display operationcarried out by the third modified version as described above. Thus, itis possible to obtain the same effects as those produced by the firstand second embodiments as well as the first and second modifiedversions.

As described above, in the case of the multi-view system according tothe third modified version, first and second video images different fromeach other are displayed alternately on a time-division basis as well asindividually to the first and second viewers respectively. It is to benoted that the present invention can also be applied to a case in whichthree or more video images different from each other are displayedindividually to three or more viewers in the same way. In addition, thenumber of video images different from each other does not have to beequal to the number of shutter-spectacle sets each worn by a viewer.That is to say, a plurality of shutter-spectacle sets each put in anopen or close state can be provided for one video image so that thevideo image can be viewed by the same plurality of viewers each wearingone of the shutter-spectacle sets.

3-3: Other Modified Versions

Each of the first and second embodiments as well as the first to thirdmodified versions has been explained as a typical implementation of thepresent invention. However, implementations of the present invention areby no means limited to the first and second embodiments or the first tothird modified versions. That is to say, each of the first and secondembodiments as well as the first to third modified versions can befurther modified in order to implement the present invention.

In addition, it should be understood by those skilled in the art that avariety of modifications, combinations, sub-combinations and alterationsmay occur, depending on design requirements and other factors as far asthey are within the scope of the appended claims or the equivalentsthereof.

For example, as described above, each of the first and secondembodiments as well as the first to third modified versions implements a3D video-image display system which makes use of shutter glasses toserve as a typical time-division driving system. However, the presentinvention can also be applied to a color video-image displayapparatus/system which adopts typically the field sequential method. Inthe color video-image display apparatus/system adopting the fieldsequential method, one frame period is divided into 3 sub-periodsallocated to typically the three primary colors, i.e., the R (red), G(green) and B (blue) colors respectively. Video images of the R, G and Bcolors are written into the display screen sequentially during theirrespective sub-periods. In addition, a backlight radiates R, G and Blight rays synchronously with the operations to write the video imagesof the R, G and B colors respectively into the display screen. That isto say, in the case of the first and second embodiments or the first tothird modified versions, a plurality of video images different from eachother are a left-eye video image and a right-eye video image which havea disparity but, in the case of this color video-image displayapparatus/system adopting the field sequential method, a plurality ofvideo images different from each other are three video images of the R,G and B colors.

In addition, as described above, each of the first and secondembodiments as well as the first to third modified versions implements atypical liquid-crystal display apparatus which employs a liquid-crystaldisplay panel configured to include liquid-crystal devices. However, thepresent invention can also be applied to a display apparatus of anotherkind. To put it more concretely, for example, the present invention canalso be applied to a display apparatus employing a PDP (Plasma DisplayPanel) and a display apparatus employing an EL (Electro Luminescence)display panel.

The series of processes described previously in the explanation of eachof the first and second embodiments as well as a variety of modifiedversions described so far can be carried out by hardware and/orexecution of software. If the series of processes described above iscarried out by execution of software, programs composing the softwarecan be installed into a general computer or the like. As an alternative,such programs can also be stored in advance in a storage medium embeddedin the general computer.

1. (canceled)
 2. A video-image processing apparatus comprising: avideo-image processing section configured to execute output control on aplurality of video-image streams each including a plurality of unitaryvideo images so as to output every unitary video image pertaining toeach of said video-image streams repeatedly a plurality of times in arow by sequentially switching said video-image streams to be output fromone stream to another; a frame memory for temporarily storing animmediately preceding unitary video image as it is or after replacingthe luminance gradation of said immediately preceding unitary videoimage with a post-replacement luminance gradation where said immediatelypreceding unitary video image is defined as a unitary video image whichimmediately leads ahead of a current unitary video image being output bysaid video-image processing section; and an overdrive processing sectionconfigured to carry out overdrive processing on said current unitaryvideo image in accordance with said luminance gradation of saidimmediately preceding unitary video image already stored in said framememory and the luminance gradation of said current unitary video image,wherein a unitary video image pertaining to each of said video-imagestreams is output repeatedly a plurality of times in a row in the sameplurality of output operations; in said overdrive processing carried outon said current unitary video image output in any one of said outputoperations, said overdrive processing section refers to a lookup tableused for prescribing an overdrive quantity set for said current unitaryvideo image in accordance with the luminance gradation of saidimmediately preceding unitary video image and the luminance gradation ofsaid current unitary video image; and a lookup table referred to in anyspecific one of said output operations is different from a lookup tablereferred to in any output operation other than said specific outputoperation, and wherein for each unitary video image the unitary videoimage is output a plurality of times in a row during a predeterminedperiod, the outputs of the unitary video image during the predeterminedperiod correspond to respective subperiods, and a plurality of lookuptables are provided for respective ones of the subperiods, the pluralityof lookup tables varying from sub-period to sub-period.
 3. Thevideo-image processing apparatus according to claim 1 wherein: saidlookup tables different from each other include a first lookup table tobe referred to in a first one of said output operations and a secondlookup table to be referred to in a second and subsequent ones of saidoutput operations; each of said overdrive quantities prescribed by saidfirst lookup table is set in said first lookup table at a value whichincreases a difference in luminance gradation between said immediatelypreceding unitary video image and said current unitary video image; andeach of said overdrive quantities prescribed by said second lookup tableis set in said second lookup table at a value used in fine adjustmentcarried out after said overdrive processing performed for said firstoutput operation to sustain the luminance gradation of said currentunitary video image at the gradation of said target luminance or to makethe luminance gradation of said current unitary video image equal to thegradation of said target luminance.
 4. The video-image processingapparatus according to claim 1 wherein said video-image processingsection replaces the luminance gradation of said immediately precedingunitary video image with said post-replacement luminance gradation inorder to generate a replacement unitary video image and stores saidreplacement unitary video image in said frame memory.
 5. The video-imageprocessing apparatus according to claim 4 wherein said post-replacementluminance gradation used by said video-image processing section toreplace the luminance gradation of said immediately preceding unitaryvideo image in order to generate a replacement unitary video image to benewly stored in said frame memory is prescribed by a replacement-valuelookup table to be searched by said video-image processing section forsaid post-replacement luminance gradation set in said replacement-valuelookup table at a replacement value depending on the luminance gradationof said immediately preceding unitary video image and the luminancegradation of a previous unitary video image which has been stored insaid frame memory at a time said immediately preceding unitary videoimage is processed by said video-image processing section.
 6. Thevideo-image processing apparatus according to claim 5 wherein saidreplacement-value lookup table prescribes said replacement values eachused for making a gradation transition from a high luminance gradationof said previous unitary video image already stored in said frame memoryto a low luminance gradation of said immediately preceding unitary videoimage or a gradation transition from a low luminance gradation of saidprevious unitary video image already stored in said frame memory to amedium luminance gradation of said immediately preceding unitary videoimage.
 7. The video-image processing apparatus according to claim 1wherein said video-image processing section stores said immediatelypreceding unitary video image in said frame memory as it is.
 8. Avideo-image display apparatus comprising: a video-image processingsection configured to execute output control on a plurality ofvideo-image streams each including a plurality of unitary video imagesso as to output every unitary video image pertaining to each of saidvideo-image streams repeatedly a plurality of times in a row bysequentially switching said video-image streams to be output from onestream to another; a frame memory for temporarily storing an immediatelypreceding unitary video image as it is or after replacing the luminancegradation of said immediately preceding unitary video image with apost-replacement luminance gradation where said immediately precedingunitary video image is defined as a unitary video image whichimmediately leads ahead of a current unitary video image being output bysaid video-image processing section; an overdrive processing sectionconfigured to carry out overdrive processing on said current unitaryvideo image in accordance with said luminance gradation of saidimmediately preceding unitary video image already stored in said framememory and the luminance gradation of said current unitary video image;and a display section configured to display video images on the basis ofunitary video images obtained as a result of said overdrive processing,wherein a unitary video image pertaining to each of said video-imagestreams is output repeatedly a plurality of times in a row in the sameplurality of output operations; in said overdrive processing carried outon said current unitary video image output in any one of said outputoperations, said overdrive processing section refers to a lookup tableused for prescribing an overdrive quantity set for said current unitaryvideo image in accordance with the luminance gradation of saidimmediately preceding unitary video image and the luminance gradation ofsaid current unitary video image; and a lookup table referred to in anyspecific one of said output operations is different from a lookup tablereferred to in any output operation other than said specific outputoperation, and wherein for each unitary video image the unitary videoimage is output a plurality of times in a row during a predeterminedperiod, the outputs of the unitary video image during the predeterminedperiod correspond to respective subperiods, and a plurality of lookuptables are provided for respective ones of the subperiods, the pluralityof lookup tables varying from sub-period to sub-period.
 9. Thevideo-image display apparatus according to claim 7 wherein said displaysection is a liquid-crystal display section configured to employliquid-crystal devices.
 10. A video-image display system comprising: avideo-image display apparatus for displaying video images bysequentially switching a plurality of video-image streams each includinga plurality of unitary video images from one stream to another; andshutter glasses carrying out opening and closing operationssynchronously with operations performed by said video-image displayapparatus to sequentially switch said video-image streams in order todisplay said video images, wherein said video-image display apparatusincludes a video-image processing section configured to execute outputcontrol on a plurality of video-image streams each including a pluralityof unitary video images so as to output every unitary video imagepertaining to each of said video-image streams repeatedly a plurality oftimes in a row by sequentially switching said video-image streams to beoutput from one stream to another; a frame memory for temporarilystoring an immediately preceding unitary video image as it is or afterreplacing the luminance gradation of said immediately preceding unitaryvideo image with a post-replacement luminance gradation where saidimmediately preceding unitary video image is defined as a unitary videoimage which immediately leads ahead of a current unitary video imagebeing output by said video-image processing section; an overdriveprocessing section configured to carry out overdrive processing on saidcurrent unitary video image in accordance with said luminance gradationof said immediately preceding unitary video image already stored in saidframe memory and the luminance gradation of said current unitary videoimage; and a display section configured to display video images on thebasis of unitary video images obtained as a result of said overdriveprocessing, wherein a unitary video image pertaining to each of saidvideo-image streams is output repeatedly a plurality of times in a rowin the same plurality of output operations; in said overdrive processingcarried out on said current unitary video image output in any one ofsaid output operations, said overdrive processing section refers to alookup table used for prescribing an overdrive quantity set for saidcurrent unitary video image in accordance with the luminance gradationof said immediately preceding unitary video image and the luminancegradation of said current unitary video image; and a lookup tablereferred to in any specific one of said output operations is differentfrom a lookup table referred to in any output operation other than saidspecific output operation, and wherein for each unitary video image theunitary video image is output a plurality of times in a row during apredetermined period, the outputs of the unitary video image during thepredetermined period correspond to respective subperiods, and aplurality of lookup tables are provided for respective ones of thesubperiods, the plurality of lookup tables varying from sub-period tosub-period.